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In 2011, Scallan et al. estimated the overall burden of foodborne illness caused by known and unspecified agents1.

This analysis included 31 pathogens known to cause foodborne illness and unspecified agents that cause acute gastroenteritis illnesses (AGI). Scallan et al. also estimated the number of hospitalizations and deaths caused by these illnesses.

Estimating US foodborne illnesses for 31 known foodborne pathogens

For each pathogen2, we gathered data from surveillance systems and corrected for underreporting and under-diagnosis. We then multiplied the adjusted number by the proportion of illnesses that was acquired in the United States (that is, not during international travel) and the proportion transmitted by food to yield an estimated number of illnesses that are domestically acquired and foodborne. Then, we added the estimates for each of the pathogens to arrive at a total, and used an uncertainty model to generate a point estimate and 90% credible interval (upper and lower limits) (Figure 1).

*Probability distributions were used to model uncertainty in each of the data inputs. Point estimates were bounded by a 90% credible interval.

**For six of the 31 pathogens, no routine surveillance data were available so alternative approaches were used to estimate illnesses.

Estimating US foodborne illnesses for unspecified agents

Unspecified agents fall into four general categories:

Agents with insufficient data to estimate agent-specific burden

Known agents not yet recognized as causing foodborne illness

Microbes, chemicals, or other substances known to be in food whose pathogenicity is unproven

Agents not yet described

To estimate foodborne illnesses from unspecified agents, we used symptom-based data from surveys to estimate the total number of AGI and then subtracted the number of illnesses accounted for by known gastroenteritis pathogens. We then multiplied this number by the proportion of domestically acquired illnesses and of illnesses attributable to food, just as we did for the known agents. Finally, again as with the known-pathogens estimate, we used an uncertainty model to generate a point estimate and 90% credible interval (upper and lower limits) (Figure 2).

Foodborne illnesses due to chemicals that cause acute gastroenteritis are included in the estimate of illnesses due to unspecified agents. However, chemicals or unspecified agents that do not cause acute gastroenteritis are not included in the estimates.

Estimating hospitalizations and deaths from US foodborne illnesses due to known pathogens

For each known pathogen with surveillance data available, we multiplied the estimated number of reported illnesses (after correcting for underreporting) by the pathogen-specific hospitalization and death rate from surveillance data, surveys, or outbreak data. Because some people with illnesses that were not laboratory-confirmed would also have been hospitalized and died, we doubled the estimates to correct for under-diagnosis. We multiplied the adjusted hospitalization and death estimates by the proportion of illnesses that were acquired within the United States (vs. international travel-related) and the proportion transmitted by food. Finally, we used an uncertainty model to generate a point estimate and 90% credible intervals for both hospitalizations and deaths (Figures 3 and 4).

Figure 3. Estimating hospitalizations from foodborne illnesses due to known pathogens, 2011*

*Probability distributions were used to model uncertainty in each of the data inputs. Point estimates were bounded by a 90% credible interval.

Figure 4. Estimating deaths from foodborne illnesses due to known pathogens, 2011*

*Probability distributions were used to model uncertainty in each of the data inputs. Point estimates were bounded by a 90% credible interval.

Estimating hospitalizations and deaths from US foodborne illnesses due to unspecified agents

To estimate hospitalizations, we applied the average hospitalization rate for all AGI, determined from survey data for 2000–2006, to 2006 US population estimates and subtracted the estimated number of hospitalizations caused by the 24 known pathogens that cause AGI. For deaths, we determined the death rate for acute gastroenteritis illnesses from US death certificates (specifically, multiple-cause-of-death data) for 2000–2006 and applied that rate to the 2006 US population estimate. We then subtracted the estimated number of deaths from the 24 known gastroenteritis pathogens. For both hospitalizations and deaths, we multiplied the overall number by the proportion of hospitalizations and deaths from the 24 known gastroenteritis pathogens that was domestically acquired and foodborne. Finally, we used an uncertainty model to generate a point estimate and 90% credible intervals (Figures 5 and 6).

75% of children experience an episode of clinical illness by 5 years of age

Various acute gastroenteritis data sources (see Table 6b)

Acute gastroenteritis illnesses, hospitalizations, and deaths

Norovirus

See Table 6b

See Table 6b

Fraction of acute gastroenteritis attributable to norovirus

* Passive surveillance from COVIS was used in preference to active surveillance from FoodNet for Vibrio spp. because most illnesses are reported by Gulf States (Florida, Alabama, Louisiana, Texas) that are not included in the FoodNet surveillance area.

‡ Beginning in 2000, there were 10 FoodNet sites. In 2008, the population of these sites was 46 million persons, 15% of the US population.

§ Incidence of laboratory-confirmed illnesses in FoodNet from 2004 to 2007 was applied to the 2006 US Census population estimates.

† Data from FDOSS on Streptococcus spp., Group A were included from 1996 to 2007 for illnesses and from 1981 to 2007 for hospitalizations and deaths because of a paucity of data (Appendix 1 and 3).

# Giardia intestinalis became nationally notifiable in 2002.

Table 6b. Data sources used to estimate illnesses, hospitalizations, and deaths due to acute gatroenteritis in the United States, 2011 (from Scallan et al.)

Data source

Data

Definition

Geographic coverage

Time frame

FoodNet Population Survey

Rate of illness

Average annual rate of acute gastroenteritis was derived by multiplying the average monthly prevalence by 12, where an episode of acute gastroenteritis was defined as diarrhea (≥3 loose stools in 24 hours) or vomiting in the past month with both lasting >1 day or resulting in restricted daily activities. Persons with a chronic condition in which diarrhea or vomiting was a major symptom and persons with concurrent symptoms of cough or sore throat were excluded.

FoodNet sites‡

2000–2001, 2002–2003, 2006–2007

Death certificates -- Multiple-cause-of-death data from the National Vital Statistics System